Non-discoloring antidegradants

ABSTRACT

Compounds of the formula   WHERE R is secondary of tertiary alkyl and X is straight or branched chain primary, secondary, or tertiary alkyl which are excellent non-discoloring antidegradants for rubber polymers.

United States Patent 1 Young et a1.

[451 Sept. 25, 1973 N ON-DISCOLORING ANTIDEGRADANTS [75] Inventors: EvanJohnson Young; Charles Gene Summers, both of Medina, Ohio Related U.S.Application Data [62] Division of Ser. Nos. 609,335, Jan. 16, 1967, Pat.No.

3,505,287, and Ser. NO. 871,106, Aug. 1, 1969.

[52] U.S. Cl 260/619 A [51] Int. Cl. C07c 39/16 [58] Field of Search260/619 A [56] References Cited UNITED STATES PATENTS 2,791,616 5/1957Luten 260/619 A 2,647,102 7/1953 Ambe1ang..... 260/619 A UX 3,211,65210/1965 Hinkamp 260/619 A X 2,748,181 5/1956 Jackson et a1. 260/619 A UX2,947,789 8/1960 Ambelang 260/619 A 2,899,394 8/1959 Palfreeman 260/619A X 3,068,198 12/1962 Haines et a1 260/619 A X FOREIGN PATENTS ORAPPLICATIONS 744,004 10/1966 Canada 260/619 A OTHER PUBLICATIONSAmbelang et a1., J.A.C.S., V01. 75 (1953) 947-950.

Primary Examiner-Bemard Helfin Attorney-Richard O. Zerbe, J. E; Maurerand Neal E. Willis [57] ABSTRACT Compounds of the formula OH CH:

where R is secondary of tertiary alkyl and X is straight or branchedchain primary, secondary, or tertiary alkyl which are excellentnon-discoloring antidegradants for rubber polymers.

1 Claim, No Drawings 1 NON-DISCOLOR ING ANTIDEGRAIDANTS This applicationis a division of application Ser. No. 609,335 filed Jan. 16, 1967, nowUS. Pat. No. 3,505,287, and a division of application Ser. No. 871,106filed Aug. 1, 1969 now U.S. Pat. 3,620,980;

BACKGROUND OF THE INVENTION The invention pertains to the field ofantidegradants for olefin and diolefin polymers. Certain specifichydroxy compounds are known antidegradants. Known hydroxy compoundsinclude bridged cresols of which the compound4,4'-butylidenebis(6-tert-butyl-m cresol) is a rubber antioxidanttrademarked Santowhite Powder. Santowhite Powder is a member of a familyof antioxidants prepared by reacting a 2,5-dialkyl phenol with analdehyde. The number position and kind of alkyl strongly influenceantioxidant efficiency. Reacting aldehydes with dialkyl phenols havingthe alkyl groups in positions other than the 2- and S-position mayresult in compositions not useful as antioxidants according to BeaversU.S. Pat. No. 2,816,945 of Monsanto Company (1957). Ambelang studied thereaction of 2,5-dialkyl phenols with aldehydes to produce 4,4-alkylidenebis(fi-tert alkyl-m-cresols). The Structure and Configurationof Dihydroxydiphenylmethanes Derived from Butylated m-Cresols asEvidenced by Infrared Absorption, Journal of the American ChemicalSociety 75, 947 (1953). He suggests the existence of unsymmetricalbis-6-tert-alkyl-m-cresols in which the alkylidene bridge is in the2-position in one ring and in the 4-position in the other. No use forthe products is disclosed. The compound4-hydroxymethyl-2,6-di-tertbutylphenol is a rubber antioxidanttrademarked lonox 100. The compound 2,6-di-tert-butyl-4-methyl phenol isa rubber antioxidant trademarked lonol. British Patent 927,179 of theEthyl Corporation published May 29, 1963, discloses methylenebis phenolsand their use as antioxidants having at least one tertiary alkyl groupof 4 to 9 carbon atoms positioned ortho to hydroxy and at least onehydroxy positioned para to the methylene bridge. Insofar as the patentdiscloses methylenebis dialkyl phenols, all 4 alkyl groups are adjacentto hydroxy or three of them are adjacent to hydroxy and one para tohydroxy. The compound 4,4'-methylenebis(2,6-ditert-butyl-phenol) is arubber antioxidant trademarked Ethyl Antioxidant 702. The compound 2,2-methylenebis-(4-methyl-6-tertbutyl phenol) is an antioxidant trademarkedAntioxidant 2246. In the methylenebis 2,4-dialkyl phenols, it is pointedout by Davis that increasing the size of the methylene bridge adverselyaffects the activity of the compound as an antioxidant. U.S. Pat. No.2,538,355 of the American Cyanamid Company (1951 An antidegradant whichis non-discoloring to a polymer and has good stabilization againstoxygen degradation is necessary for raw polymers. The compound andcompound mixtures of our invention display both of these properties.They are at least equivalent to the most effective prior art compoundsin both properties and superior in one.

SUMMARY Compounds of the formula where R is secondary or tertiary alkyland X is straight.

or branched chain primary, secondary, or tertiary alkyl, are excellentnon-discoloring antidegradants for rubber polymers. Mixtures containingisomers of these compounds are also excellent non-discoloringantidegradants.

In the rubber industry it is customary to add an antidegradant duringcompounding of vulcanizable stocks. Polymers obtained by solution oremulsion polymerization must be protected immediately afterpolymerization because they may be stored in bales of raw polymer for amonth or more before the polymer is compounded and cured for consumeruse. The baled polymer must contain a stabilizer to prevent degradation.When consumer use is for a white pigmented or non-filled polymerproduct, the baled raw polymer is useless for this purpose if it hasbecome discolored. The use of compounds or mixtures of this invention inraw polybutadiene provides a non-discolored polymer with goodstabilization against oxygen degradation. The use of compounds ormixtures of this invention in raw polybutadiene is an improvement overthe prior art.

Antioxidant 2246 discolors polybutadiene during aging. Santowhite Powderis essentially non-discoloring in polybutadiene but is derived from therelatively scarce and expensive meta-cresol. The new bridged cresols arenon-discoloring to the baled raw polymer and more effective stabilizersthan Santowhite Powder. At the same time economy in production isachieved. The most economical antioxidants comprise compound mixtureswhich contain as essential ingredients the new unsymmetrical bridgedcresols.

An example of the new compound is 2-[alpha,alpha-(4-hydroxy-2-methyl-5-tert-butyl phenul)butyl]-6-tertbutyl-p-cresol ofthe formula CH3 CH2 HIC" HrC-- CHa The mixtures containing the newcompounds may be prepared by reacting a mixture of 6-alkyl-m-cresol andZ-aIkyl-p-cresol with an aliphatic aldehyde of 2 to 7 carbon atoms. Forexample, mixtures of compounds obtained when about 2 parts of alkylatedm-cresol and 1 part of alkylated p-cresol are bridged with an alkylidenegroup of 2 to 7 carbons, and in which the alkyl group on the cresolscontains from 4 to 12 carbon atoms are excellent stabilizers. An exampleof this type of mixture is the reaction product obtained when a mixtureof tert-butyl-m-cresol and tert-butyl-p-cresol is bridged withn-butyraldehyde. This mixture contains 2 ,2 '-butyli-denebis( 6-tert-butyl-p-cresol 4 ,4 butylidenebis(6-tert-butyl-m-cresol) and 2-[alpha,alplfa-(4-hydroxy-2-methyl-5-tert-butyl phenyl-)-butyl1-6-tert-butyl-p-cresol.

PREFERRED EMBODIMENTS To prepare 2-[alpha,alpha-(4-hydroxy-2-methyl-5-tert-butyl phenyl)butyll -tert-butyl-p-cresol, 82 grams (0.5 mole) ofZ-tert-butyl-p-cresol and 82 grams (0.5 mole) of 6-tert-butyl-m-cresolare charged into a gas sparger equipped reaction flask. Methanol (100ml.) is added and gaseous hydrogen chloride (0.4 mole) is fed into thestirred solution for about 1 hour. Forty grams of n-butyraldehyde (0.56mole) is added in 1 hour at 45C. The reaction mixture is stirred anadditional 2 hours at 6070C. The reaction mixture is cooled to 30C. and100 grams of water is added and the mixture is stirred. After stirringfor 5 minutes, the aqueous phase decanted. The organic phase is washedwith two 150 gram portions of water. At this stage of the process, thebatch may be steam sparged to remove residual tert-butyl-m-cresol andtert-butyI-p-cresol. The reaction product contains about 41%2-[alpha,alpha-(4- hydroxy-2-methyl-5 -tert-butylphenyl)-butyl]-6-tertbutyl-p-cresol, about 27.7%4,4-butylidenebis(6-tertbutyl-m-cresol), and about 26%2,2'-butylidenebis(6- tert-butyl-p-cresol). The product mixture isslurried in 100 grams of hydrocarbon solvent and filtered to remove4,4-butylidenebis(o-tert-butyl-m-cresol). The filtrate is warmed to3040C. and treated with about 5 grams of Super Filtrol clay fordecolorization. Filtrol is a trademark for chemically treated colloidalclay for decolorizing and purifying. The mixture is filtered and thefiltrate is vacuum stripped up to about 100C/30 mm Hg. The product isrecrystallized with a hydrocarbon solvent to isolate the compound2-[alpha,alpha-(4- hydroxy-2-methyl-5-tert-butylphenyl)-butyl]-6-tertbutyl-p-cresol. Twenty-seven grams of the whitesolid compound is obtained. The melting point of a sample recrystallizedtwice in hydrocarbon solvent is 130131C. The empirical formula of thecompound is C I-1 0 The molecular weight is 382.59. The compound elutesat 260C. on a programmed vapor phase chromatograph when 4,4-butylidenebis(6-tert-butylm-cresol) elutes at 270C. Other compounds ofthis invention are prepared in a similar manner to the preparationdescribed above.

The mixtures from which the compounds of this invention are isolated arevaluable antioxidants. However, it is preferred to employ a higher ratioof 6-tertbutyl-m-cresol to decrease discoloration problems in thepolymer. Also, mixtures of mand p-cresols in a ratio of about 2:1 areavailable from coal tar fractions and are economical to use.

Essentially non-discoloring economical mixtures of compounds comprise byweight to 50% 4,4- alkylidenebis(6-tert-alkyl-m-cresol), 10 to 2,2-alkylidenebis(6-tert-alkyl-p-cresol), and 40 to 55% 2-[alpha,alpha-(4-hydroxy2-methyl-5tert-alkylphenyl)alkyl]-6-tert-alkyl-p-cresol.Antioxidant efficiency and safety from discoloration are improved byisolating and using the last named component but in most instances themixtures are satisfactory. The first named component is insoluble inpetroleum hydrocarbon solvents. The major portion of it can be removedby treating the reaction product with a petroleum hydrocarbon solventand removing undissolved solids by filtration. The mixtures of thisinvention are prepared in a similar manner to the preparation describedabove. The ratio of the cresols may vary.

An example of a mixture preparation is the reaction of 2 parts oftert-butyl-m-cresol and 1 part of tert-butylp-cresol withn-butylraldehyde. The mixture product of this reaction contains about14% 2,2'-butylidenebis(6- tert-butyl-p-cresol), about 48%4,4'-butylidenebis(6- tert-butyl-m-cresol), and about 42%2-[alpha,alpha-(4- hydroxy-2-methyl-5-tert-butylphenyl)butyl]-6-tertbutyl-p-cresol. In a vapor phase chromatographicanalysis of the mixture, the elution time for 2,2-butylidenebis(o-tert-butyl-p-cresol) is three minutes, for2-[alpha,alpha-(4-hydroxy-2-methyl-5-tertbutylphenyl)butyl]-6-tert-butyl-p-cresol is 4.15 minutes, and for4,4'-butylidenebis(6-tert-butyl-m-cresol) is 6.15 minutes. The analysisis carried out in a four foot column with a A inch diameter. The columnis packed with 3% silicone gum rubber (trademarked SE-52) on ChromosorbW. Chromosorb W is a trademark for a white diatomaceous earth support.The temperature of the column is 260C. The carrier gas is helium. Theflow rate of the helium is 125 ml/minute.

A mixture of this invention is prepared by alkylating 2 parts ofm-cresol and one part of p-cresol with Gulf Propylene Trimer. GulfPropylene Trimer is a narrow boiling C olefin fraction obtained from thecatalytic polymerization of propylene. It is a liquid highly reactivemonoolefin, low in peroxides and sulfur, and suitable for alkylation andother olefinic reactions. Alkylation is effected by heating 10 grammols. of the cresol mixture, 12.5 gram mols. of propylene trimer, and104 grams of Retro], and acid activated absorbent clay, at 108130C. Thereaction is continued until 68% conversion to alkylate and then thereaction mixture is distilled. The mixture of 6-nonyl-m-cresol and2-nonyl-pcresol, B. P. 188-200C/30 mm Hg, is bridged withn-butyraldehyde in the manner previously described. Products prepared byalkylating mixtures of mand pcresol upon condensation with an aldehydeyield mixtures of this invention substantially identical to thoseprepared from mixtures of pure alkyl-m-cresol and pure alkyl-p-cresol.

Stabilizers of this invention are mixed with raw solution or emulsionpolymers while the polymers are in their dissolved or emulsified state.Solvent is evaporated from the solution polymer at room temperature. Thesolution polymer can be steam distilled to remove solvent. In steamdistillations, lower boiling antidegradants such as Ionol often distillout of the polymer. It is advantageous to use compounds or mixtures ofthis invention when steam distillation is used because they do notdistill out of the polymer. The emulsion polymer is isolated from waterby coagulation. The polymers are then milled at 50C., blended nine timesat a mill setting of 0.008 in., then sheeted out between 1/16 and inchthickness. The sheets are cut into 25 to 30 samples and aged in acovered pan. Color and Mooney Viscosity data are obtained from thesesamples.

The stability of raw polymers wherein the compounds or mixtures of thisinvention are used is measured by the change in Mooney Viscosity. TheMooney Viscosity Test has the American Society for Testing MaterialsDesignation, D1646-63. The data below illustrate aging of raw polymerswith and without the stabilizers of this invention. Data for knownantioxidants are included for comparison purposes.

Color is evaluated by visual observation. In color tests, the mostdesirable color is colorless. The code for the color characteristics in'the Tables below is as follows:

C Colorless LY Light Yellow VLY Very Light Yellow A Amber LA Light AmberVLA Very Light-Amber B Equal to Untreated Polymer In some instancestherubber itself is colored and B designates thatthe treated polymer isequal to the untreated control. Company X, Company Y, and Company Z inthe Tables stand for commerical polybutadiene from differentmanufactures. The unstabilized polybutadiene cements of Company X andCompany Y are light amber color. Company Zs unstabilized polybutadienecement is colorless.

TABLE I.POLYBU'IADIENE AGING, 100 C.

Samples of Polybutadiene containing compound 2-[alpha,-alpha-(4hydroxy-2-methyl-5-tert-butylphenyl)butyll-6-tert-butyl-p-cresol and Ionol were aged at PolybutadieneCompany X Company Y Aging time, Mooney Color, Mooney Color, Compound at0.5 phr. hrs. viscosity 48 hrs. viscosity 48 hrs.

Antioxidant 2246 0 42 DA 2,2-butylidcnebis-(4-n1ethyl-G- tert-butylphenol) 0 42 DA Mixture of this invention 1 0 45. 5 B 42 B 2-[alpha,alpha-(4'hydroxy-2-rnethyl-5- tert-hutyl phenyl)butyl]-6-tert=butyl-pcresol 0 43 B Snntowhite powder 0 43 B 'Blank.. 0 16 30 (l 48 lThe mixture contains 18% 2,2'-buty1idenebis(6-tcrt-bntyl-pcrcs0l, 53% 2-alpha, alpha- (4-hydroxy-2-methyl-fi-tert-hutyl phcnylhutylHi-tcrt-butyl-p-crcsol and 17 a 4,4"hutylidenebis(6-tcrt-hutylm-crcsol).

I Crumbled on mill.

2 Antioxidant 2246 3 2-[ alpha,alpha-( 4- hydroxy-2-me thyl-S-tert-bntylphenyl)butyll fi-tert-butyl-p-cresol 4 Santowhite Powder 5 Ionol 6 BlankC. for 10 days. The data in Table llll illustrate that Company YsPolybutadiene survived even this severe treatment when this compound ofour invention is used. Stock 1 contains 2-[alpha,alpha-(4-hydroxy-2-methyl-5-tert-butyl-phenyl)butyl]-6-tert-butyl-pcresol, and stocks 2 and3 contain lonol.

TABLE III Stock 1 2 3 Mooney Viscositiea at l00C after Aging at 100C.for: initial 37 37 36 5 days 71 l54 153 10 days l 13 Brittle Thepolybutadiene stocks in Table lV contain the following:

O kllhb) The compounds and mixtures of this invention are usefulantioxidants in cured polymers. The data in Tables V and V1 illustratewhite natural rubber vulcanizates containing2-[alpha,alpha-(4-hydroxy-2-methyl- S-tert-butylphenyl)butyl]-6-tert-butyl-p-cresol and mixtures of this inventioncompared to a blank and Santowhite Powder. The natural rubbervulcanizates in Tables V and V1 contain the following:

Parts Pale Crepe Rubber 100.0 Zinc Oxide surface treated with PmpionicAcid 25.0 Titanium Dioxide Filler 50.0 Stearic Acid 1.0 Antioxidant 2.0

The Ozone data in Table V indicate the time to 80 percent retentionduring dynamic ozone exposure. The method used for measuring the ozonedamage to vulcanized rubber is described by Decker and Wise, The StressRelaxation Method for Measuring Ozone Cracking," Rubber World, April,1962, page 66. The Ultimate Tensile Strength data in Tables V and V1 arein pounds/in'. The samples are aged in an aluminum block at 100C. 1

TABLE V ultimate tensile strength ozone to at at 80% Unaged 24 hrs. 48hrs. retention Blank 3500 2600 1800 50 2-[alpha,alpha-(4- hydroxy2-methyl-5- tert-butyl phenyl) butyll-6-tert-butyl-pcresol 3400 29002600 64 Santowhite powder 3500 2800 2400 42 Mixture of this invention3500 3100 2400 59 Mixture of this invention" 3400 3000 2300 52 Themixture contains 18% 2,2'-butylidene-bis(6-tert-butyl-p-cresol), 53%Z-lalpha,alpha-(4-hydroxy-2-methyl-5-tert-butyl phenyl)butyl]-6-tert-butylp-cresol, and 17% 4,4-butylidene-bis(6-tert-butyl-mcresol).

" The mixture contains 13.7% 2,2'-butylidenebis(6-tert-butyl-pcresol),41.6% 2-[ alpha,alpha-(4-hydroxy-2-methyl-5-tert-butylphenyl)butyl]-6tert-butyl-p-cresol, and 48%4,4-butylidenebis(6-tertbutyl-m-cresol).

TABLE VI ultimate tensile strength at at Unaged 24 hrs. 48 hrs. Blank3700 2600 1800 Mixture 3500 3100 2700 Mixture 3600 3300 28002-[alpha,alpha-(4- hydroxy-Z-methyl-S- tert-butyl phenyl)-butyl]-6-tert-butyl-p-cresol 3600 3300 3000 Santowhite powder 3700 3400 3100Mixture of this invention containing the reaction product of 2 partsm-cresol and 1 part p-cresol alkylated with Gulf Propylene Trimer andbridged with n-butyraldehyde.

Mixture of this invention containing 17%4,4'-butylidenebis-(tHertbutyl-m-cresol), 18%2,2'-butylidenebis(6-tert-butyl-p-cresol), and 55%2-[alpha,alpha-(4-hydroxy-Z-methyl-S-tert-butyl phenyl)butyl]-6-tert-butyl-p-cresol.

The word alkyl which defines R on the alkylated cresol includescycloalkyl for purposes of this invention. For example, mixtures ofcycloalkylated m-cresols and cycloalkylated p-cresols can be used asstarting materials for the bridged compounds and mixtures of thisinvention. Examples of such starting materials are cyclohexyl m,p-cresol and cyclooctyl m, p-cresol.

The antidegradants of this invention are effective in polymers atconcentrations of 0.25 to 10.0 parts per hundred. Concentrations from0.25 to 3 parts per hundred are preferred. Comparable results to thosein the Tables, supra, demonstrating utility are obtained withantidegradants of this invention which are not illustrated. Theantidegradants of this invention may be used in homopolymers,copolymers, and terpolymers of olefins, diolefins, and related monomers.Antidegradant properties comparable to those illustrated inpolybutadiene and natural rubber are obtained in other polymers, forexample, styrene-butadiene rubber, butyl rubber, ethylene-propylenediene monomers, polyethylene, polypropylene, and copolymers of butadienewith other monomers such as styrene, acrylonitrile, isobutylene, ormethyl methacrylate.

It is intended to cover all changes and modifications of the examples ofthe invention herein chosen for purposes of disclosure which do notconstitute departures from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The compound 2-[alpha,alpha-(4-hydroxy-2- methyl-5-tert-butylphenyl)butyl]-6-tert-butyl-pcresol.

